This application claims the priority benefit of Taiwan application serial no. 88114801, filed Aug. 30, 1999.
1. Field of the Invention
The invention relates in general to a color meter. More particularly, this invention relates to an imaging-splitting color meter at an optical entrance pupil.
2. Description of the Related Art
To inspect the quality of color, a color meter has been broadly applied to various industries as an instrument for quality inspection and management of color. Referring to FIG. 1, a conventional color meter is schematically illustrated. An observing object 10 reflects a light beam after being incident with a light source, for example, a light emitting diode (LED) or a television screen. This incident light source is converged by a converging lens 20 and restricted by an entrance pupil 30, and then forms an image on a photodetective plane 40. The observing object 10 and the photodetective plane 40 are conjugate image points, that is, the observing object 10 is an object plane of the optical system, while the photodetective plane 40 is the image plane of the optical system.
After the photodetective plane 40, multiple photosensors 50 are disposed. As shown in FIG. 1, color filtering devices 80 (color filters in general) are used to filter red light (R), green light (G), and blue light (B). Being filtered, these lights are then received by the photosensors 50 which can also detect the light intensity of these lights. Therefore, different signals are generated according to various colors with different light intensities. These signals are then transmitted from an amplifier 60 to an electronic system 70, the color of the observing object 10 can thus be measured and calculated.
The chromaticity of three colors R, G and B are calculated by the electronic system 70 according to the intensities of the light signals thereof. Different methods of color filtering have been developed currently, for example, {overscore (xa+L )}, {overscore (xb+L )}, {overscore (y)} and {overscore (z)} coloring filters of human vision; red (R), yellow (Y), green (G), cyan (C) and blue (B) color filtering method; and visible range multi-wavelength color filtering method. These above functions can be achieved using photosensors of different observing objects.
In FIG. 2, assuming that the observing object A is partitioned into three portions a1, a2 and a3, and an image of the object A is formed onto the photodetective plane 40, that is, on B. The photodetective plane B is also partitioned into three portions b1, b2 and b3 to dispose photosensors for R, G and B lights, respectively. If the colors are uniformly distribute over the object A, the distribution of lights on the photodetective plane B is substantially uniform as well. Under this circumstance, the arrangement of the photosensors of various colors would not be affected. However, if the color distribution in the portions a1, a2 and a3 of the object A is non-uniform, and consequently the color distribution of the portions b1, b2 and b3 is non-uniform, the arrangement of the photosensors is then impacted.
For example, human eyes are synthetically uniform against color. Therefore, the color of the object A observed by the human eyes is an average of the colors in A, that is, an average aave of a1, a2 and a3. In the photodetective plane B, b1 receives the light from a1, b2 receives the light from a2 and b3 receives the light from a3. When the position of the photosensors is out of place, the color calculated is not equal to an average value bave of b1, b2 and b3. Thus, the color detected by the photosensors is not real.
Referring to FIG. 3, a non-uniform color distribution of an object is illustrated. Assuming that the signals R=B=G, that is, a1=a3=a3, the color aave that the observer sees is white.
FIG. 4 and FIG. 5 illustrate a result of a poor arrangement of photosensors in the photodetective plane. The red dash line circles the location of a red color filtering device and a red photosensor. The green dash line circles the location of a green color filtering device and a green photosensor, and the blue dash line circles the location of blue color filtering device and a blue photosensor.
In FIG. 4, only blue light can transmit through the blue color filtering device to be received by the blue photosensor. The green light can not pass through the red color filtering device, so that the red photosensor can not receive any signal. The red light cannot pass through the green color filtering device, so that there is nothing received by the green photosensor. As a result, being analyzed by the electronic system, the light of the object is blue instead of white.
In FIG. 5, the photosensors are turned with an angle. A small portion of the blue light can pass through the blue color filtering device and received by the blue photosensor. An even smaller portion of the red light can pass through the red color filtering device to be received by the red photosensor. However, both of the blue light and the red light can not transmit through the green color filtering device, so that the green photosensor can not detect any signal. Being analyzed by the electronic system, the object is in purple color instead of being white.
Therefore, when the color distribution of an object to be observed is non-uniform, the arrangement of photosensors greatly affects the analysis of the electronic system. The above problems happen to the color inspection of textile, fabric, ceramic tiles with uneven surface or metal.
To resolve the above problems, methods have been proposed such as:
(a) Using a diffuser:
Referring to FIG. 6, a diffuser is used between the entrance pupil 30 and the photodetective plane 40 to mitigate the effect caused by non-uniform color distribution. The diffuser, though improves the uniformity, reduces the efficiency of light due to the diffusion.
(b) Using a photoconductive optic fiber:
Referring to FIG. 7, photoconductive optic fiber is disposed on the photodetective plane 40. The light focused onto the photodetective plane 40 is coupled into the photoconductive optic fiber to be conducted into various color filtering device 80 to the corresponding sensors 50. Again, this method greatly enhances the uniformity but reduces the efficiency of light.
(c) Using an integrating sphere:
Referring to FIG. 8, an integrator sphere is installed on the photodetective plane 40. The light converged at the photodetective plane 40 is conducted into the integrator sphere 110, and passes through the color filtering device 80 to reach the photosensors 50. This method uses scattering of light to improve the uniformity. Though the improvement of uniformity is the best among these methods, the efficiency is poor, and the cost is high, the volume is large.
The invention provides an image-splitting color meter. An image splitting device is disposed at an entrance pupil to improve the uniformity of light with a high efficiency.
The image-splitting color meter provided by the invention comprises a light converging device, an image-splitting device, multiple color filtering devices and a photosensor including multiple color sense devices. The light converging device is used to restrict an incoming light beam from an observing object. The image-splitting device is disposed at an entrance pupil to split the incoming light beam into multiple split light beams. The color filtering devices are used to receive the split light beams, so as to convert these split light beams into corresponding color light beams. The color sensors receive the corresponding color light beams and transform these color light beams into electrical signals.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.